In recent years a vehicle including an automatic transmission is known that reduces a burden on a driver operating a brake in a traffic jam and the like. More specifically, when the vehicle is stopped in a forward position and in that condition once the vehicle has the brake pedal operated to a degree (e.g., in an amount) larger than a predetermined degree, then thereafter even if the brake pedal is not operated the braking force applied when the vehicle is stopped is held (i.e., brake hold control is exerted). In starting a vehicle subjected to the brake hold control, when the driver releases his/her foot from the brake pedal, a force applied to brake the vehicle when the vehicle is stopped is held. Furthermore, the vehicle subjected to the brake hold control is adapted such that when the driver operates the accelerator pedal the brake hold control can be cancelled to start the vehicle. Thus in starting the vehicle on an uphill road when the driver releases his/her foot from the brake pedal the vehicle does not reverse and is thus readily started. In starting the vehicle on a downhill road, when the accelerator pedal is pressed the brake hold control is cancelled, and the acceleration attributed to the engine and that attributed to the downhill road are simultaneously exerted and the vehicle may suddenly start. To resolve this problem, for example Japanese Patent Laying-Open No. 10-329671 discloses a technique.
Japanese Patent Laying-Open No. 10-329671 discloses a brake control system including a brake hold function. More specifically, when a vehicle is stopped and the driver releases his/her foot from the brake pedal, the function holds a braking pressure applied from a master cylinder linked with the brake pedal. The brake control system includes a gradient determination unit determining a gradient of a road at least from a degree of operation of an accelerator pedal of the vehicle, and a control unit exerting control to release the held braking pressure if the road's gradient is a downhill gradient.
According to Japanese Patent Laying-Open No. 10-329671, the brake control system allows a road's gradient to be determined at least from a degree of operation of an accelerator pedal and if the gradient is a downhill gradient a held braking pressure is released. Thus in starting the vehicle on a downhill road the held braking pressure has been released. The acceleration attributed to the engine and that attributed to the downhill road are not simultaneously exerted and the vehicle can avoid suddenly starting.
For example, to detect a driver's request for acceleration more precisely, a degree of operation of an accelerator pedal that has attained a predetermined value, rather than the accelerator pedal being simply operated, may be considered as the driver's request for acceleration and the brake hold control may accordingly be cancelled. However, when the brake hold control is cancelled, and if at that time a driving force having a magnitude corresponding to the degree of operation of the accelerator pedal that has the predetermined value has been output, the vehicle may suddenly start.
However, Japanese Patent Laying-Open No. 10-329671 is silent on how the brake control system operates for canceling brake hold control when a degree of operation of the accelerator pedal attains the predetermined value.